1. Field of the Invention
This invention pertains to a computer input system. More specifically, the invention pertains to a stylus used in conjunction with a capacitance sensitive computer input pad (touch pad) which measures the magnitude of a capacitive disturbance caused by an object touching the touch pad surface. The tip of a stylus is placed in contact with the touch pad surface and a mannually manupulable element of the stylus enables a user to adjust the magnitude of capacitive disturbance which the stylus creates on the touch pad surface.
2. State of the art
Many computer input devices have been developed to accommodate the different object positioning sensing methods and apparati available. In the field of touch sensitive computer input pads (touch pads) in particular, various object sensing and position determining technologies have been used and refined to increase reliability and accuracy. For example, pressure sensitive touch pads enabled any object which could be pressed against the touch pad surface at a localized point and then moved along the surface to cause a corresponding movement of a cursor on a computer display. A stylus has often been integrated with the touch pad to provide a pointing device other than a finger. The stylus provides certain advantages which a finger cannot, and is therefore preferred over a finger in certain applications. By pressing firmly against the touch pad with the tip of a stylus, a user can develop the same pressure against the touch pad as a finger. Unfortunately, various drawbacks with pressure sensitive touch pads have limited their use.
Object position sensing technology is not limited to pressure sensitive devices. For example, other position sensing approaches include infrared sensing, acoustic wave sensing, piezoelectric force sensing, electromagnetic sensing, electrostatic sensing, sonic pulse sensing and capacitive sensing. A stylus is typically used with these sensing technologies, for example, when the intuitive feeling of a pen-like device is preferred such as in an application requiring "painting" or "drawing" with a computer. Another situation where a stylus is preferred is when other more cumbersome input devices cannot be used such as where the user is mobile and where handwriting recognition software is available.
The physical properties of the particular stylus used in conjunction with the above technologies varies. For example, on a pressure sensitive touch pad, the stylus may be any object which provides a relatively well defined point which can be clearly "seen" by the sensing technology. Such a stylus is taught in U.S. Pat. No. 5,365,598 issued to Sklarew. Disadvantageously, the stylus is required to make good contact at all times with the touch pad to minimize adding resistance that would lower the voltage detected by the touch pad, and result in an erroneous position determination. Therefore, the user must be careful to apply sufficient and consistent pressure, but without damaging the touch pad. The stylus position is determined by sensing the voltage in an X and Y axis on a conductive sheet on which the stylus is pressed. Voltages will vary with the distance of the stylus tip from the conductive edges of the touch pad surface.
Other position sensing and determining technologies are responsive to both the touch of a finger and an inanimate object such as a stylus. U.S. Pat. No. 5,365,461 issued to Stein et al. is an example of such a device. In particular, this invention apparently teaches that it is possible to distinguish between the human touch and the touch of the inanimate object. The preferred embodiment applies the capacitive sensing technology which enables the inanimate object to be detected by supplying a current to the object and then determining the current flow though the object into the conductive coating. Necessarily, the stylus is conductive. However, the conductivity cannot be modified.
This and other advantages of capacitance sensitive touch pads has resulted in several variations to try and improve the technology. For example, U.S. Pat. No. 3,921,166 issued to Volpe teaches a capacitive matrix which the touch of a finger can cause to vary the transcapacitance of the touch pad.
In a similar manner, U.S. Pat. No. 4,455,452 issued to Schulyer teaches a capacitive touch pad where a finger attenuates the capacitive coupling between touch pad electrodes.
A patent which specifically addresses a stylus was issued to Rympalski as U.S. Pat. No. 4,639,720. The stylus is said to alter the transcapacitance coupling between touch pad electrodes.
U.S. Pat. No. 5,149,919 issued to Greanias teaches a system whereby a stylus position is determined by detecting which matrix wires are carrying the strongest signal, thus indicating the position of the stylus tip.
Much of the detail about the styli used in conjunction with the references above describes how the styli can cause some type of capacitive disturbance which is detectable by the touch pads. This disturbance is caused, for example, by supplying a voltage to the stylus tip as in Stein et al. The Sklarew patent also refers to other styli which can use light in the form of ultraviolet, infrared or even microwave which is scanned by the touch pad, as well as resistive, capacitive or inductive coupling with the styli. It is important to remember that the present invention, however, is limited to capacitance sensitive touch pads such as the one taught in Gerpheide, U.S. Pat. No. 5,305,017. The Gerpheide patent discloses devices and methods which overcome the drawbacks inherent in other devices which utilize a sensing tablet or sensing surface. The devices and methods of the Gerpheide patent include a touch sensitive input pad upon which a user conveniently inputs position information by positioning the user's finger tip in close proximity to the top surface of the position sensing surface of the touch sensitive pad. The device of the Gerpheide patent detects the position of the finger tip in the x and y directions of the touch pad as well as the finger's proximity in the z direction in relation to the sensing surface. In addition to a finger, the pointing object can be any other conductive object such as the stylus which is the subject of the present invention.
The present invention is limited to capacitance sensitive touch pads for several reasons. First, it is useful to recognize one significant limitation common to the styli which work with capacitance sensitive touch pads. This limitation is related to the position sensing technology being either an "on" or "off" binary result. In other words, the stylus is either in contact with the touch pad, or it's not. Therefore, it is unknown in the art to provide more information from the stylus other than its position as determined by the sensing technology.
It would therefore be an advantage over the state of the art to provide a stylus which works on a capacitance sensitive touch pad which can provide more information to the touch pad/computer system than its location without adding to the complexity of the stylus or affecting its reliability. It would thus be an advantage to provide a stylus which could provide this greater amount of information through a simple mannual adjustment. It would also be an advantage to provide this greater amount of information without resorting to providing power to the stylus and thereby increasing complexity, bulk and cost. It would be a further advantage to provide this greater amount of information without having to add hardware external to the stylus body.